This invention pertains to an apparatus and method useful in the commercial growing of marine organisms.
There is a great interest in the world today in establishing new and controllable sources of protein for human needs. Marine organisms, of which fish are an example, are an important food source that man is seeking to domesticate and grow commercially. A commercialization approach which controls and confines the fish or other marine life for the major portion of their life span is most desirable in view of the pressures currently being placed on world fisheries. Also, having a reasonably predictable harvest is necessary to a viable commercial fish growing operation.
One approach to the commercialization of growing of marine organisms consists of holding and feeding young organisms until maturity or marketable size is reached. The confinement must be such that a proper environment is maintained in which the organisms can grow. Sufficient growing space, food, oxygen and waste disposal must be provided. Generally, the economics of commercial operations require that high population densities be maintained, which crowding creates difficulties in maintaining optimum growth rates.
This invention is concerned with the above-described commercialization method in which juvenile fish of a single species are introduced to a flexible net enclosure suspended into a body of water such that the fish are confined within a relatively constant volume of water. A natural or artificial current ensures a constant supply of oxygen and water-borne nutrients by the free passage of the water through the net sides and bottom of the enclosure. Food is introduced into the net pen from the surface while excess food and waste products are carried away by the currents. The fish are held in the pens until they reach maturity or marketable age, at which point they are harvested.
As expected, the economics of commercialization make desirable a high population density. The density of the fish within a given area is limited by the ability of the enclosure and its supporting systems to provide the necessities of space, food, oxygen, and waste removal within optimum growing ranges. The total fish population is limited by the ability of the operating unit to manage or physically handle the equipment and supplies.
The supporting apparatus of this invention provides stiffening members such that a net enclosure suspended from it maintains its intended shape below the surface of the water. A constant volume for enclosing the growing fish is therefore defined, eliminating any significant billowing or collapse caused by current movements through the net. The supporting apparatus thereby ensures that the design volume or confinement space is attained, allowing the highest possible total population therein.
During the long fish growing period, marine plants, such as seaweeds and algae, attach themselves to the net to the extent that flow through the pens is impeded. Eventually, the impediment due to marine growth is great enough to decrease the available oxygen supply to the fish and to prevent the currents from adequately removing waste products and uneaten food. Both the decrease in oxygen supply and inadequate waste removal must be taken into account in establishing permissible population densities, and operate to limit the economic viability of the commercial fish rearing operations. Fish, of course, must have available a certain specific amount of oxygen to sustain life. Failure of oxygen supply results in death or at least requires a reduction of the fish population to the level for which sufficient oxygen is available. Failure of the flushing currents to remove waste provides breeding grounds for harmful bacteria, threatening the population with disease, therefore further limiting population densities.
Elimination of the adverse effects of the marine growth problem without harm to the fish has generally involved some method of periodic cleaning of the net pens. Previously, this might require that divers scrub the net walls, either hydraulically or mechanically, to remove the marine organisms. Since the adverse effects from fouling begin to return as soon as one week after cleaning, in fertile tidal waters, this method has not proved satisfactory because of the expense and time consumption involved.
The supporting apparatus of this invention allows a method for rapidly exchanging clean nets for fouled enclosures while confining the fish population below the surface in a temporarily reduced volume, without loss of or harm to them. The method provides a simple exchange means which can be accomplished from the surface and which requires only a low labor input. Consequently, the exchange method may be utilized with the frequency necessary to eliminate the marine fouling limitation on population densities by ensuring a free flow of water through the selected enclosure. With the properly sized enclosures, the supporting apparatus allows the changing of nets by hand with only one or two individuals. Power equipment such as lifting devices and winches may be utilized in conjunction with the supporting apparatus-enclosure as the size of the system increases.
In its most basic form, the purpose of this invention is to define a supporting apparatus, a plurality of which forms a supporting structure for suspending a flexible enclosure into a body of water such that the enclosure defines a constant volume below the surface of the water such that a product contained within the enclosure is prevented from escaping. The supporting apparatus of the invention is so designed that the vertical depth of the enclosure is adjustable. Further, the supporting apparatus is so designed that the containment enclosures may be kept free of marine growth that interfere with the free passage of water by providing a method of exchange of clean nets for fouled enclosures without necessitating the prior removal of the fish population.
The supporting apparatus allows, in combination with a properly sized net, exchange of the net enclosures with a minimum of labor such that the exchange can be made frequently enough to maintain the free passage of waters through a clean enclosure as is necessary for optimum growing conditions.